1. Field of the Invention
The present invention relates to a method for creating an equivalent circuit and a program for creating an equivalent circuit. More particularly, the present invention relates to a method and a program for creating an equivalent circuit for a three-terminal capacitor.
2. Description of the Related Art
Simulation can be used in design of circuits of electronic devices and in design of printed circuit boards. In the simulation, models of equivalent circuits of electronic components, such as three-terminal capacitors, are often incorporated in the circuits of the electronic devices for use. For example, an equivalent circuit illustrated in FIG. 9 is known as an exemplary equivalent circuit for a three-terminal capacitor in related art. FIG. 9 is an equivalent circuit diagram of a three-terminal capacitor in the related art.
The three-terminal capacitor in FIG. 9 includes resistors R500, R501, R502, and R504, coils L500, L501, and L502, a capacitor C500, and outer electrode 502a to 502c. The resistor R500, the coil L500, the resistor R501, and the coil L501 are connected in series between the outer electrodes 502a and 502b. The resistor R502, the capacitor C500, and the coil L502 are connected in series between a connection portion between the coil L500 and the coil L501 and the outer electrode 502c. The resistor R504 is connected in parallel to the capacitor C500.
In the equivalent circuit illustrated in FIG. 9, it is difficult to precisely simulate a circuit board on which the three-terminal capacitor is mounted, as described below. FIG. 10 illustrates how a three-terminal capacitor 500 is mounted on a circuit board 508.
The three-terminal capacitor 500 includes four outer electrode 502a, 502b, 502d, and 502e, as illustrated in FIG. 10. The outer electrodes 502a and 502b are generally used as input and output terminals. The outer electrodes 502d and 502e are generally used as a ground terminal. Such a three-terminal capacitor 500 is mounted on the circuit board 508. More specifically, the circuit board 508 includes land electrode 510a to 510d. The outer electrodes 502a, 502b, 502d, and 502e are joined to the land electrodes 510a to 510d, respectively.
However, the outer electrodes 502d and 502e are considered as one outer electrode 502c in the equivalent circuit in the related art. Accordingly, the impedance between the land electrodes 510c and 510d is not considered in the simulation using the equivalent circuit in the related art. In addition, since the parasitic inductance and the parasitic capacitance in the land electrode 510c are different from those in the land electrode 510d when the land electrode 510c has a shape different from that of the land electrode 510d, the current flowing through the outer electrode 502d differs from the current flowing through the outer electrode 502e. The difference in current is not also considered in the equivalent circuit in the related art. Accordingly, it is difficult to precisely simulate the entire circuit board 508 on which the three-terminal capacitor 500 is mounted.
For example, a method of optimizing circuit constants described in Japanese Unexamined Patent Application Publication No. 2004-71642 is known as a technology concerning equivalent circuits in the related art. However, no description of precise simulation in a circuit using a three-terminal capacitor exists in Japanese Unexamined Patent Application Publication No. 2004-71642.